Patent Literature 1 describes, with an aim to “suppress a temperature rise in an inverter while avoiding generation of electromagnetic noise as much as possible”, that “a PWM mode selection unit 280 normally selects an asynchronous PWM, whereas when an element temperature Tsw of an inverter 14 rises, it selects a synchronous PWM. A carrier wave control unit 270 sets a carrier frequency fc during the asynchronous PWM to a relatively high prescribed frequency by which the electromagnetic noise is less likely to be detected, whereas it sets the carrier frequency fc during the synchronous PWM based on a rotational frequency ωe such that a periodicity (carrier number) k of carrier waves included in one period of an electrical angle of an AC motor M1 according to a mode selection of the PWM mode selection unit 280”.
Now, in a situation where a stopped state of a vehicle is maintained, such as while waiting for a traffic signal, a state may take place where an electric motor used in a brake control device has a rotary speed of zero (rotation angle maintaining a certain value) and outputs torque (which is called a locked state). In a case where braking is performed intensely (case where a braking operation is large) under this locked state, excessive current continues to be supplied over a long period of time to one of three coils and to a switching element for supplying electricity to this coil. From the aspect of temperature rise in the coil and the switching element, such a situation is desirably avoided.